This project will characterize brain angiotensin H (AII) receptor subtypes. The ultimate goals this project will be to determine the AII receptor subtypes mediating the various functions of AII in the brain. The rationale for these studies derives from recent observations that sulfhydryl reducing agents inhibit binding to one of the brain AII receptor subtypes. Since most studies of brain AII receptor binding have been done in the presence of sulfhydryl reducing agents, only one the of the brain AII receptor subtypes has been studied in detail. The specific aims of this project are to identify agents that act as selective agonists at brain AII receptor subtypes, to pharmacologically characterize the AII receptor subtypes, to determine if additional AII receptor subtypes occur in the brain, to determine the effects of sulfhydryl reactive agents on brain AII receptors, to determine if brain AII receptors couple to G proteins, and to examine functional responses to agonists and antagonists of AII administered directly into the brain. For functional studies, selective antagonists for one subtype will be given prior to the agonist to preclude mediation of the response by that subtype. Angiotensin II acts in the brain primarily to regulate fluid and electrolyte balance, however, it is also thought to have additional functions. The discovery of subtypes of AII receptors in the brain, may indicate that discrete, noncardiovascular functions for AII will be discovered. Since many brain diseases still have unknown etiologies, disturbances in brain angiotensinergic function could play a role in such disorders. The methods to be used in this project are peptide synthesis using FMOC techniques to prepare AII receptor subtype selective of analogs AII, radioligand binding assays, including in vitro receptor autoradiography to determine the AII receptor subtype profile of brain-nuclei. Binding assays will be done in the presence of ligands and conditions selective for individual AII receptor subtypes; and in vivo testing of responses, e.g., dipsogenesis and blood pressure changes, to angiotensins directly administered into the rat brain. The radioligand binding data will be analyzed by nonlinear regression procedures capable of determining and evaluating binding constants for multiple receptor subtypes. In vivo testing procedures will compare the efficacy of AT1, and AT2 receptor subtypes selective AII analogs in the absence and presence of All receptor selective antagonists by Students's t tests.